In a most general sense most wheel chairs driven by electric motors are presently being controlled by a control device which has a manually operable control stick and this is connected to a number of switches to control the direction of drive of each of the motors and variable resistors by which the speed of the motors in either a forward or rearward direction can be effected.
In practice, the resistors deteriorate very quickly because of constant wear of wipers on resistance material and even with the highest quality materials such rapid wear is experienced.
Furthermore, contacts in switches also deteriorate in the constant use situation applicable in such applications as wheel chairs, and it has been experienced that such units need constant and indeed expensive replacement.
Applicant is aware of attempts to overcome this problem in such cases as that illustrated in U.S. Pat. No. 3,814,199 in which a mask is used to control the amount of light falling onto a detector from an emitter located on the other side of the mask.
No practical application of such a concept has been seen but a number of difficulties do result from such a proposal.
For instance, an off condition of any motor is established by the mask fully stopping light falling onto a particular detector but at the same time, the detector must be sensitive enough to commence drive of the respective motor upon a very small additional light falling on the detector.
The motor control speed is governed by varying the degree of light falling on the detector and the full range of motor speeds therefore must be able to be obtained by varying the light by covering a selected portion of the detector.
This means of course that very small differences in position of a mask must result in significant changes in motor speed, and therefore the device becomes very sensitive to even slight vibration or to manufacturing tolerances and also of course any spurious reflections.
The device will also of course be quite sensitive to the voltage supplied to the light or radiant energy emitter in that this will directly affect the motor speed if it increases or decreases and it therefore would appear not to be a clearly satisfactory answer.
Indeed it is shown in one application, especially shown in FIG. 14 of this patent, that a resort to off/on contacts for forward and rearward speed control of the motor is suggested as a preferred answer.
In another attempt to solve the same problem, applicant is aware of U.S. Pat. No. 3,934,181 in the name of Rosenthall.
This also includes a mask however with a more sophisticated attempt to provide less sensitivity in the control by providing specifically shaped cutouts in the mask but this apparatus also suffers from the same problems as those experienced in the previous apparatus and there is obviously required great skill in devising some cutout shaping to provide good control of the motor speed which can provide proportionate control of the two motors so as to ensure an accurate direction of drive of the wheel chair.
Once again, no practical application of the apparatus is known to the applicant and it is believed that it is an apparatus and incorporates circuitry which has significant difficulties still.